what better reason than 'for science?
by Miah-Chan
Summary: Oikawa huffs, ruffling his bangs over his forehead, and pouts at Hajime as he says slowly, "Haven't you been listening, Iwa-chan? We should practice kissing!"


A very belated happy birthday to the lovely **astersandstuffs**! ❤

Many thanks to everyone in the CSG for their helpful comments & editing!

 **Disclaimer:** I do not own "Haikyuu!" or any affiliated characters.

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Hajime's having a good day. Practice went well, he's more or less caught up with his summer homework, he has a part-time job lined up to help pay for the new volleyball gear he'll need for his first year at Aoba Johsai—everything is falling into place nicely.

So he should have known Oikawa would manage to disrupt it somehow.

 _Honestly_ , only Oikawa Tooru would announce with no preamble whatsoever:

"Iwa-chan, we should practice kissing!"

Hajime barely manages to keep the swig of water he just took _in_ his mouth (he wouldn't be surprised if Oikawa _planned_ that) and looks up from his textbook to stare incredulously at his best friend.

He's on the floor, lying on his stomach with his feet kicking back and forth in the air childishly as he studies the page of the magazine open before him. He's propped himself up on his elbows, hands cradling his chin as he reads, looking entirely too nonchalant about what he just suggested.

(And unfairly _pretty_ with the way the afternoon sunlight is highlighting everything from his hair to his eyes and cheekbones; the way it dips beneath the loose neckline of the T-shirt he's wearing, creating shadows along his collarbone that Hajime just wants to—)

Forcing himself away from that train of thought, Hajime finally asks, "What're you on about?"

Oikawa glances up at him with a wide smile (and there is _definitely_ a cunning edge to it) as he taps the magazine with his index finger.

"We should practice! This article has some techniques that sound interesting—"

"The hell are you reading over there?" interrupts Hajime, bewildered. He pushes away from where he's been leaning against the space under the open window, crawling forward to peer down at the article's title.

 _Kissing tricks that will drive him crazy!_

"Why are you even reading this?" he asks, sitting back on his knees as he raises a brow at the brunet. Oikawa lifts a shoulder in a shrug, his smile never wavering (though his cheeks seem a bit pinker).

"Nee-san gave some to me as a joke and you were all in 'study mode' so I was bored," he explains, looking back at the page. He hums, tapping his finger again at something. "We could probably skip this one since it's kinda basic—"

"Whoa, wait, timeout." Hajime waves his hands in front of him as if it'll wave away this crazy idea Oikawa's throwing at him. "What's this _we_ stuff?"

Oikawa huffs, ruffling his bangs over his forehead, and pouts at Hajime as he says slowly, "Haven't you been listening, Iwa-chan? We should practice kissing!"

"And why should we do that?" demands Hajime, quirking a brow.

Oikawa's answer is immediate. "For science."

"For science," Hajime echoes, deadpan. They stare at each other for a moment; Hajime tries to gauge how serious Oikawa actually is as the boy in question simply waits. Before long a Cheshire-like grin tilts his lips and he leers playfully at Hajime.

" _Ooh_ , maybe we _should_ start with the basics if Iwa-chan is so _shy_." He waggles his eyebrows in a terrible attempt at what Hajime assumes he thinks is flirty—mainly succeeding in just looking like an idiot, in Hajime's humble opinion—and Hajime can't help but roll his eyes (while unsuccessfully keeping the blush he can feel blooming on his cheeks at bay).

"I am _not_ but that's not even the point, you idiot." He crosses his arms over his chest, peering down his nose at Oikawa's smirking face. "Why do we, specifically you and I, have to practice _together_?"

Oikawa lets out a long-suffering sigh, rolling his eyes towards the ceiling as if it may hold all the answers as to why Hajime is apparently too dense to understand what is obviously a simple situation.

"Iwa-chan, do you _want_ to embarrass yourself in the event that someone ever decides they want to kiss you? Just imagine!" He gasps and claps his palms against his cheeks theatrically. Hajime rolls his eyes. "You go in with no experience and it's _terrible_ and now you've got to live out the remainder of your life in shame or hiding–what if you have to become a _hermit_ , Iwa-chan, how awful! Living out the rest of your sad, lonely, embarrassing life in solitude because once upon a time you _scorned_ Oikawa-san's most generous offer to help you gain experience."

There's silence between them for a few moments, both looking at the other seriously, before Hajime snorts, clamping a hand over his mouth to muffle the laugh he feels bubbling up his throat. A few chuckles slip between his fingers as he grins and shakes his head at his best friend. Oikawa yelps an offended "hey!" but Hajime ignores it.

"You are such a drama queen!" he exclaims when he's caught his breath. He drops his hand from hiding the grin that still lingers and exhales slowly, shrugging in defeat. "Fine."

' _It's not like all our firsts haven't been with each other anyway_ ,' he thinks fondly, if not a little wistfully. ' _Besides, I'd be lying if I said I don't_ want _this_.'

Oikawa stares at him with a look that's partially affronted, partially shocked, before a smile lights up his entire expression. Hajime's momentarily taken-aback by how _genuine_ it is before Oikawa is scrambling to sit up, clutching the magazine between his fingers as he scoots over to kneel in front of Hajime.

"Okay, so!" he points at the first paragraph detailing how to begin. "I understand the basics but since Iwa-chan is _clearly_ a newbie—"

"You know I can change my mind at any time, right?" Hajime interrupts casually, adjusting so he's sitting with his legs crossed instead.

Oikawa whines at him, insisting, "You can't back out now, Iwa-chan!"

He doesn't need to know that that's the _last_ thing Hajime wants to do.

"Just c'mere," Hajime sighs, leaning forward with his elbows on his knees. Oikawa glances at the magazine one more time before placing it on the floor and turning to mirror Hajime's position.

"It uh...It said to start out with pecks and—" he murmurs as he fidgets with the hem of his shorts, betraying his nerves (leave it to Oikawa to flaunt his bravado even when he's actually as lost as everyone else). Hajime doesn't hesitate in reaching to take the setter's hands in his, brushing his thumbs over the backs comfortingly while he jokes, "What are we, chickens?"

It does the trick and Oikawa laughs, the tension in his shoulders evaporating. They smile at each other for a moment, blushes darkening their cheeks at the proximity, until both are overcome with embarrassment and quickly tilt their heads forward at the same time—effectively headbutting each other.

"Oww!" they groan simultaneously, pulling back. Hajime releases one of Oikawa's hands to rub at the bridge of his nose, glowering at his friend. Oikawa rubs the back of his neck sheepishly, chuckling—and then he leans forward again to place a chaste kiss against Hajime's forehead in apology. It's a light brushing of lips but Hajime feels his heart start to pound in his chest anyway, heat overtaking his entire face. Oikawa pulls back and giggles at the cherry shade.

"I _knew_ Iwa-chan was shy!" he trills triumphantly. Hajime narrows his eyes.

' _I'll show_ you _shy_.' he thinks, leaning forward to press his lips against that smirking mouth. Oikawa makes a noise of surprise but presses back. It only lasts a moment; Hajime pulls away so _he_ can smirk at Oikawa's wide-eyed expression and the blush rapidly spreading down his neck.

"Iwa-chan!" he gasps, scandalized. "N-No fair, we were supposed to do it together!"

"Pretty sure there aren't any rules to this," Hajime points out. Oikawa gapes at him and then pouts, looking away as his blush darkens. Hajime snickers.

" _Now_ who's shy?" he gloats, proud. Oikawa's gaze snaps back to Hajime at that; immediately, he sees the words ignite a fire of competitiveness in Oikawa's eyes and he doesn't have time to consider just where this might lead as Oikawa leans forward in a way that can only be described as _predatory_.

"Hmmm? Iwa-chan thinks he's clever but that was a pretty poor attempt," he purrs, leaning forward so that he's completely in Hajime's space. He doesn't even realize he's leaning away until he finds himself lying back with only his elbows to support him. Oikawa smiles, and there's that _cunning_ edge to it that Hajime had caught a glimpse of at the beginning of all this; he presses closer, having gotten to his knees so he can crawl forward.

Suddenly, Oikawa's straddling Hajime's lap, steadying himself with warm hands on Hajime's shoulders. He slides them over the slopes of Hajime's shoulders until he links them behind his neck, thumbing the fine hairs there, sending electricity down Hajime's spine. He holds back a shiver at the touch, keeping his gaze on Oikawa's half-lidded stare, waiting for his next move.

(He knows they've started something they won't be able to take back _and he doesn't care_.)

"If you're such an expert," Hajime finally breathes out softly, the air between them warm. "You shouldn't need to practice."

"Maybe I don't." Oikawa replies, fingers twitching against Hajime's nape. He licks his lips, Adam's apple bobbing as he swallows thickly; Hajime wants to trail kisses up and down that pale throat _so badly_ but—

 _'Priorities, Hajime_.'

Hajime breathes in deep, his chest brushing against Oikawa's, and exhales the words before he can change his mind, "Then why are we doing this?"

He wants to take them back immediately because he _wants this_ , has wanted this for two years, but even in this position he has to _know_ it's what Oikawa wants too. So many of the important things between them can be left unsaid; they have no need for voicing them when they simply _understand_ , but this…

Hajime can't take a chance on something this important.

Oikawa breathes out slowly through his nose, warming the air between them as he presses closer so that their chests are flush; Hajime can feel the pounding of Oikawa's heart, a rapid rhythm betraying the nerves he won't show. Instinctively, Hajime raises one hand to smooth it over Oikawa's waist in an attempt at comfort. Oikawa chuckles breathlessly, eyes fluttering at the touch, and his smile is somehow both timid and daring.

"Because," he finally answers, voice soft and hoarse, "I _really_ want to. And I think you do too."

Hajime feels his heart leap at the admission, joy flooding his veins; he grips Oikawa's hip to ground himself, studying those brown eyes for any sign of dishonesty. He's delighted when he finds none.

"Yeah," he answers, throat tight with emotion. Oikawa's eyes light up and Hajime can't help but grin. "So are we gonna practice or…?"

" _Please_ ," Oikawa gasps, fingers tightening against Hajime's neck reflexively, and Hajime needs no further prompting. He surges up, pushing into a sitting position so he's free to use his hands, and brings them up to cup Oikawa's face as he leans in.

This kiss is better, perhaps because it lasts for more than five seconds or because they both know the other truly _wants_ it; either way, Hajime revels in the feel of Oikawa's soft lips, warm and plush against his own slightly chapped ones. He presses closer, smoothing his thumbs over the arch of Oikawa's cheekbones, tilting his head just so. He feels Oikawa unlace his fingers from behind his neck so he can run them through Hajime's hair instead, a soft moan against his lips making his brain short circuit. He pulls away reluctantly but rests their foreheads together, opening his eyes slowly to find Oikawa still coming to. He watches the way his eyelashes flutter before revealing dark brown eyes, still somewhat unfocused, and can't help the smile that takes over.

Elated, nervous giggles bubble up his throat, and he tries to subdue them but it's no use.

' _I just kissed Oikawa Tooru_.' he thinks giddily, gazing into his best friend's eyes with what he's sure is the sappiest, most dumbfounded expression, but he can't help it. ' _Oikawa just kissed me. He_ wants _to kiss me_.'

As always, they're of the same mind because Oikawa is smiling, giggles of his own spilling from his lips _—wet_ and _pink_ because _I just kissed him_ _holy shit_ —as he brushes his nose against Hajime's, the gesture sweet. Loving.

"Again," he whispers, and now Hajime can feel the trembles of his hands where they move over his shoulders. " _Again_ , Iwa-chan, please."

And when has Hajime refused Oikawa anything?

They meet again, lips brushing feather-light before pressing more firmly, heartbeats racing in their chests. Oikawa brings his hands up to cup Hajime's jaw, breathing in sharply when Hajime releases his cheeks to card fingers through his hair, other arm looping around his waist to pull him closer.

There's no space left between them as they explore one another, finding the angles and pressure that works best, pulling back only to dive back in–hearts too full of excitement and wonder of _this is really happening_ to pause for too long.

Oikawa hums against Hajime's mouth, pulling away just slightly so he can murmur against his lips, "Wanna try something."

"Hmm?" Hajime hums, unsure if it's a question or demand, taking the opportunity to kiss across Oikawa's cheeks, his brow, his eyelids and nose. Oikawa giggles again at the attention, using his hold on Hajime's face to pull him away so he can focus on his new objective. Hajime pouts at him but the look in Oikawa's eyes tells him they have all the time in the world for more of that later.

"Trust me?" Oikawa asks—which is ridiculous, really, because _of course Hajime does_ but he understands the need for certainty so he nods. Oikawa makes a happy sound, and Hajime can feel his smile against his lips before they're pressing against his again insistently.

(Impatient, too, but that's no surprise considering it's Oikawa. Hajime finds he doesn't mind much this time.)

Oikawa frames Hajime's face between his hands, cupping his jaw in his palms and pressing his fingertips gently against his jawline as he finds a rhythm that he likes. Hajime doesn't mind following—he never has, not if it's with Tooru—so when Oikawa parts his lips just a bit, Hajime does the same.

It's no secret that Oikawa Tooru is a perfectionist to the core so it isn't long before he's found exactly the angles, the pressure, the amount of tongue and lip nipping that makes Hajime's hands fist into the back of his shirt so he can pull him even closer. Oikawa kisses him deeper, sliding a hand into his hair for an experimental tug, and Hajime can feel the self-satisfied smirk against his mouth when he unintentionally groans in pleasure. His face feels like it's on fire with embarrassment—where did the bashful Oikawa from earlier go, the one who was worried over _pecks_ of all things?—but he'll be damned if he lets that stop them.

Oikawa pulls away from his mouth to press hurried kisses along the line of Hajime's jaw, using the hand in his hair to tip his head to his liking as he moves towards Hajime's earlobe. The first scrape of teeth makes Hajime's heart leap, heat coiling in his stomach, but Oikawa seems to have another destination. Hajime squeezes Oikawa's hips, unsure of what else to do but hold on as he lets Oikawa have his way.

The press of lips against his neck feels good, the slide and pressure fanning the flame growing in his belly, so he doesn't really notice at first that Oikawa has paused in one spot—too caught up in the newness of sensation and the awe that _this is happening_ in the first place.

But then there's more pressure and the graze of teeth again—and suddenly Hajime knows _exactly_ what Oikawa's doing.

Hajime slides his hand up Oikawa's back to grab the collar of his shirt and _yanks_ , pulling him away from his neck with a growl too breathless to be very threatening, "Oi, what the hell Shittykawa!"

Oikawa lets himself be manhandled so that he's sitting further back on Hajime's lap, a good distance away from his neck. Still, he whines at the action, crossing his arms over his chest with a pout that puffs his cheeks.

(He looks like a ruffled hamster, with his hair all awry from Hajime's fingers, but no matter how endearing Hajime can't let it sway him.)

" _Eehhh_ , Iwa-chan I wasn't done!" he complains, jutting out his lower lip. He peers at his work before sighing in disappointment, "Damn, it's already disappearing." Hajime claps a hand over the spot that's still tingling, trying to focus on why he stopped Oikawa in the first place.

"You can't just leave hickies all over me, you jerk," he grumbles. Oikawa huffs, glancing off to the side as he mutters something under his breath. Hajime raises a brow and bounces his knee once to jostle him for his attention.

"What was that?"

"I _said_ , I want everyone to know Iwa-chan is finally mine now!" exclaims Oikawa, turning his gaze back to Hajime's defiantly. Hajime feels another headrush coming on from the blush blooming over his cheeks and down his neck; Oikawa's just so _honest_ , leaving no room for doubt what he wants.

"D-Dumbass, you can't–there are other ways to—" he pauses, breathing deep to regain some semblance of composure, before muttering, "I wouldn't really care but I have to start that job next week and it's too hot to wear anything that would cover it."

Oikawa gasps, bouncing slightly in his lap before he laughs, throwing his arms around Hajime's neck in a hug strong enough to unbalance them and send them tumbling to the floor. He's still tittering in the crook of Hajime's neck; he can feel his smile against his skin.

"Silly Iwa-chan, that's what concealer is for." comes Oikawa's muffled response. Hajime chuckles, shaking his head as he cards his fingers through Oikawa's hair (he's going to have a fit later when he sees the poofy mess it's become).

"You're impossible," he answers, tugging gently on the strands as a reprimand. He feels Oikawa's smile widen into a grin before the brunet pops up onto his forearms so he can lean over Hajime with a mischievous smirk, brown eyes twinkling with glee.

"So what you're saying is, I _can_ leave them as long as they're someplace you can cover them." he says, waggling his eyebrows suggestively. Hajime gives him a blank look and flicks his forehead.

"Pervert. I should have known you'd be insatiable," he says and there's absolutely nothing he can do to hide the fondness in his voice. Oikawa must hear it too because the teasing in his eyes fades away to a soft look with a smile Hajime's only dreamed of having directed at him. He leans down to rub noses and when he speaks again it comes out hushed, breathless, awestruck.

"But you love me anyway."

Hajime wraps his arms around Oikawa's waist, leaning up to nuzzle him back, not even trying to hide the smile so wide it almost hurts.

"Yeah," he breathes. "I do."

Oikawa inhales sharply, like he wasn't expecting such a blatant admission, before he's kissing Hajime fervently—again, and again, and again. And Hajime doesn't hesitate to meet him for each and every one. 

...

"Hmm, I _knew_ Iwa-chan gave in too quickly. You must really like me~" Oikawa trills some time later as they're cuddled together on the bed with some movie playing in the background (though they've been too busy making-out to actually watch it).

"Shut up, you're the idiot who wanted to use 'practice' as an excuse to kiss me. How cliché can you be?" Hajime teases, nipping playfully at his earlobe. Oikawa gasps theatrically, smacking his chest in offense, though he doesn't pull away even a centimeter.

"Mean, Iwa-chan!"

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I hope you enjoyed! Please let me know what you thought ^^

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